This invention generally relates to ink jet printer apparatus and methods and more particularly relates to a self-cleaning ink jet printer having ultrasonics and method of assembling same.
An ink jet printer produces images on a receiver by ejecting ink droplets onto the receiver in an imagewise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
In this regard, xe2x80x9ccontinuousxe2x80x9d ink jet printers utilize electrostatic charging tunnels that are placed close to the point where ink droplets are being ejected in the form of a stream. Selected ones of the droplets are electrically charged by the charging tunnels. The charged droplets are deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them. A gutter may be used to intercept the charged droplets, while the uncharged droplets are free to strike the recording medium.
In the case of xe2x80x9con demandxe2x80x9d ink jet printers, at every orifice an actuator is used to produce the ink jet droplet. In this regard, either one of two types of actuators may be used. These two types of actuators are heat actuators and piezoelectric actuators. With respect to heat actuators, a heater placed at a convenient location heats the ink and a quantity of the ink will phase change into a gaseous steam bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled to the recording medium. With respect to piezoelectric actuators, a piezoelectric material is used, which piezoelectric material possess piezoelectric properties such that an electric field is produced when a mechanical stress is applied. The converse also holds true; that is, an applied electric field will produce a mechanical stress in the material. Some naturally occurring materials possessing these characteristics are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
Inks for high speed ink jet printers, whether of the xe2x80x9ccontinuousxe2x80x9d or xe2x80x9cpiezoelectricxe2x80x9d type, must have a number of special characteristics. For example, the ink should incorporate a nondrying characteristic, so that drying of ink in the ink ejection chamber is hindered or slowed to such a state that by occasional spitting of ink droplets, the cavities and corresponding orifices are kept open. The addition of glycol facilitates free flow of ink through the ink jet chamber. Of course, the ink jet print head is exposed to the environment where the ink jet printing occurs. Thus, the previously mentioned orifices are exposed to many kinds of air born particulates. Particulate debris may accumulate on surfaces formed around the orifices and may accumulate in the orifices and chambers themselves. That is, the ink may combine with such particulate debris to form an interference burr that blocks the orifice or that alters surface wetting to inhibit proper formation of the ink droplet. The particulate debris should be cleaned from the surface and orifice to restore proper droplet formation. In the prior art, this cleaning is commonly accomplished by brushing, wiping, spraying, vacuum suction, and/or spitting of ink through the orifice.
Thus, inks used in ink jet printers can be said to have the following problems: the inks tend to dry-out in and around the orifices resulting in clogging of the orifices; the wiping of the orifice plate causes wear on plate and wiper, the wiper itself producing particles that clog the orifice; cleaning cycles are time consuming and slow the productivity of ink jet printers. Moreover, printing rate declines in large format printing where frequent cleaning cycles interrupt the printing of an image. Printing rate also declines in the case when a special printing pattern is initiated to compensate for plugged or badly performing orifices.
Ink jet print head cleaning apparatus are known. An ink jet print head cleaning apparatus is disclosed in U.S. Pat. No. 4,600,928 titled xe2x80x9cInk Jet Printing Apparatus Having Ultrasonic Print Head Cleaning Systemxe2x80x9d issued Jul. 15, 1986 in the name of Hilarion Braun and assigned to the assignee of the present invention. This patent discloses a continuous ink jet printing apparatus having a cleaning system whereby ink is supported proximate droplet orifices on a charge plate and/or a catcher surface ultrasonic cleaning vibrations are imposed on the supported ink mass. The ultrasonic vibrations are provided by a stimulating transducer on the print head body and transmitted to the charge plate surface by the supported liquid. However, the Braun patent does not appear to disclose use of a solvent composition to accomplish print head cleaning. Moreover, the Braun patent does not appear to clean the print head in a manner that leaves printing speed unaffected by the cleaning operation.
Therefore, there is a need to provide a self-cleaning printer having ultrasonics and method of assembling same, which self-cleaning printer allows cleaning without affecting printing speed.
An object of the present invention is to provide a self-cleaning printer having ultrasonics and method of assembling same, which self-cleaning printer allows cleaning without affecting printing speed.
With this object in view, the present invention resides in a self-cleaning printer, comprising a print head having a surface thereon; a cup sealingly engageable with the surface and defining a cavity having a fluid therein; and a pressure pulse generator in fluid communication with the fluid in the cavity for generating a pressure wave propagating in the fluid and acting against the surface, whereby the surface is cleaned while the pressure wave acts against the surface.
According to an exemplary embodiment of the present invention, the self-cleaning printer comprises a print head defining a plurality of ink channels therein, each ink channel terminating in an orifice. The print head also has a surface thereon surrounding all the orifices. The print head is capable of ejecting ink droplets through the orifice, which ink droplets are intercepted by a receiver (e.g., paper or transparency) supported by a platen roller disposed adjacent the print head. Particulate matter may reside on the surface and may completely or partially obstruct the orifice. Such particulate matter may be particles of dirt, dust, metal and/or encrustations of dried ink. Presence of the particulate matter interferes with proper ejection of the ink droplets from their respective orifices and therefore may give rise to undesirable image artifacts, such as banding. It is therefore desirable to clean the particulate matter from the surface and/or orifice in a matter that does not affect printing speed.
Therefore, a cleaning assembly is disposed relative to the surface and/or orifice for directing a flow of fluid along the surface and/or across the orifice to clean the particulate matter from the surface and/or orifice. The cleaning assembly includes an ultrasonic transducer in communication with the fluid for inducing ultrasonic pressure waves in the fluid. The pressure waves impact the particulate matter to dislodge the particulate matter from the surface and/or orifice.
In another embodiment of the invention, the cleaning assembly includes a septum in addition to the ultrasonic transducer. The septum is disposed opposite the surface and/or orifice for defining a gap therebetween. The gap is sized to allow the flow of fluid through the gap. Presence of the septum accelerates the flow of fluid in the gap to induce a hydrodynamic shearing force in the fluid. This shearing force acts against the particulate matter and cleans the particulate matter from the surface and/or orifice. A pump in fluid communication with the gap is also provided for pumping the fluid through the gap. In addition, a filter is provided to filter the particulate mater from the fluid for later disposal.
A feature of the present invention is the provision of an ultrasonic transducer in communication with the fluid for inducing ultrasonic vibrations and therefore pressure waves in the fluid to remove particulate matter from the print head surface and/or orifice.
Another feature of the present invention is the provision of a septum disposed opposite the surface and/or orifice for defining a gap therebetween capable of inducing a hydrodynamic shearing force in the gap, which shearing force removes the particulate matter from the surface and/or orifice.
An advantage of the present invention is that the cleaning assembly belonging to the invention cleans the particulate matter from the surface and/or orifice without use of brushes or wipers which might otherwise damage the surface and/or orifice.
Another advantage of the present invention is that the surface and/or orifice is cleaned of the particulate matter without affecting printing speed.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there are shown and described illustrative embodiments of the invention.